Ascorbic acid is a nutrient in apple fruit， which plays a crucial role in human health. In order to elucidate the effects of exogenous glycine betaine treatment on ascorbic acid metabolism in apple fruit during storage. 'Qiujin' apple fruit was used as the material to investigate the impact of postharvest 10 mmol/L glycine betaine dipping on changes in ascorbic acid content， key enzyme activities and gene expressions related to synthesis and oxidation regeneration pathways. The results showed that glycine betaine treatment delayed the decline in ascorbic acid content in apple fruit throughout the entire storage period. By the end of the storage， the ascorbic acid content was 8.54 mmol/kg in the betaine-treated fruit compared to 8.23 mmol/kg in the control fruit. Glycine betaine up-regulated the relative expressions of MdPGI， MdPMI， MdPMM， MdGMP， MdGME， MdGGP1， MdGGP2 and MdGGP， as well as enhanced the activities of GalDH， GalLDH， GalUR， APX， DHAR， MDHAR and GR in the ascorbic acid biosynthesis and oxidation regeneration pathways. On the 12th day of storage， compared to the control group， the activities of GalDH， GalLDH， GalUR， APX， DHAR， MDHAR and GR in the glycine betaine-treated group were 1.07-， 1.09-， 1.30-， 1.12-， 1.17-， 1.12- and 2.97-times higher， respectively. Additionally， the relative expression levels of MdGalUR， MdAPX， MdDHAR， MdMDHAR and MdGR were 1.29-， 3.00-， 1.29-， 1.45- and 2.97-times higher than those of the control group， respectively. However， glycine betaine treatment down-regulated the activity and gene expression of ascorbate oxidase in fruit. On the 12th day of storage， AO activity and gene relative expression levels in the glycine betaine-treated group were reduced by 27.97% and 28.55% compared to the control group， respectively. Conclusion: These findings suggested that exogenous glycine betaine could enhance the antioxidant capacity of ‘Qiujin’ apple fruit by activating the activity and gene expression of the key enzymes involved in ascorbic acid biosynthesis and oxidation regeneration pathways.